1. Field of the Invention
This invention relates to a new device for measuring the warp yarn tension of a woven fabric in a loom which, by using an interchangeable fixed structure acting on a limited central warp band of a width always less than the minimum width of the fabric to be formed and being hence independent of the width of said fabric, achieves effective, economical, reliable and in particular repeatable measurement of said tension, without the need for perfect positioning of said
structure on the loom and hence of easy attainment. The term "repeatable measurement" is used in the sense that the measuring device continues to provide for the same fabric an identical tension value even on numerous different looms and independently of the width of the fabric under formation or of the length of the loom used, the invention concerning substantially an improvement to the measuring device described by U.S. Pat. No. 5,355,912 by the present applicant.
2. Discussion of the Background
As is well known, in a loom the warp yarn tension must be always maintained constant and hence be constantly measured and continuously adjusted, otherwise it could vary as the delivery of said yarn by the beam proceeds, because the radius of the yarn wound on the beam decreases whereas the angular velocity of the latter remains constant, the tangential delivery speed of the warp yarn hence decreasing, with consequent increase in the yarn tension.
U.S. Pat. No. 5,355,912 application it is not the warp yarn tension which is measured but instead the tension of the fabric under formation, this however being practically the same as that of the warp yarns given what said yarns are directly connected to the fabric, said tension being determined indirectly by measuring the elastic deformation which it generates on the fixed deviation bar for the fabric under formation. In other words, the measuring device of said U.S. Pat. No. 5,355,912 consists substantially of a deformation sensor which is fixed onto the fixed fabric deviation bar supported by the fixed loom frame only at its ends, to measure an elastic deformation value caused by the warp yarn tension over the entire length of the bar, this value being compared in a comparator with a set value to control the geared motor of said beam.
Such a known device, besides involving considerable constructional difficulty in fixing a sensor to a bar which generally has a minimum length of the order of 2 meters, with consequent cost increase, has in particular the drawback of providing a warp yarn tension value which is influenced by the constraints to which the fixed deviation bar for the fabric under formation is subjected, and hence not allowing precise determination of the tension to which each individual warp yarn is subjected.